1. Field of the Invention
The invention relates to electromagnetic transmission and detection, and more particularly, to waveguides and sensors for electromagnetic wave transmission and reception.
2. Description of the Related Art
Microwave technology has long been known to be useful in telecommunications and radar systems. With the proliferation of low-cost microwave semiconductor technology, however, old applications are being revisited to take advantage of the advances and new applications are being developed. In telecommunications, microwaves carry information, such as for telephone and television systems. Microwaves, which have a higher frequency than ordinary radio waves, can carry more information. In addition, because of their high frequency, microwaves can be accurately focused in a narrow beam from a transmitting antenna to a receiving antenna. Similarly, the high frequency of microwaves makes them suitable for focused radar applications.
Microwaves, like other electromagnetic radiation, may propagate through space, but may also be directed or guided. Microwaves are typically generated by an emitter and coupled to a waveguide, and are similarly received by a sensor, such as an E-field probe, coupled to a waveguide. The received signals are then directed to appropriate instruments for further processing.
Conventionally, signals corresponding to microwaves are transmitted to and from the processing circuitry via a coaxial cable system, which is connected to an assembly which matches the wave to the waveguide mode and impedance. For example, referring to FIG. 4, microwave energy is collected (or excited) in a conventional launch by an electric field (E-field) coupling probe (or emitter) 400 disposed in a waveguide 402 (or resonator), such as a circular or rectangular waveguide. The E-field probe 400 or emitter is attached to a coaxial connector 404. A non-waveguide coaxial cable is then suitably connected to the connector 404 to transmit the signals to and from the processing circuitry. Thus, the launch is configured to provide a transition between the waveguide 402 and other transmission systems.
Preferably, the launch matches the waveguide's 402 wave orientation, field type, mode, and impedance to and from the processing circuit. The probe 400 exchanges energy between the transmission line and the waveguide 402. The E-field probe 400 is typically configured as a linear, open-ended antenna which is positioned near the maximum magnitude of the electric field in the waveguide 404 and oriented so that its length is parallel to the electric field vector in the waveguide 402. Properly configured, the launch may minimize the RF power loss and maximize the power delivered to and from the processing circuit.
Although this configuration may be effective in some applications, the assembly includes several inherent drawbacks. For example, the configuration is costly, partly due to the number of components and the close tolerances for properly assembling the launch and waveguide. In addition, conventional launches or adapters require intermediate connection between the waveguide and the processing circuit. Consequently, additional connectors and cable are necessary to transmit or receive signals in conjunction with an actual processing circuit, such as a microstrip circuit board. These components not only add cost, but tend to degrade the performance and reliability of the launch.